High temperature stabilizing lubricant additive



United States Patent 3,184,408 HIGH TEMPERATURE STABILHZWG LUBRICANT ADDITIVE Ernest V. Wilson and Harry W. Rudel, Roselle, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Dec. 14, 1961, Ser. No. 159,457 5 Claims. (Cl. 252-325) The present invention relates to compounded lubricating oils that are stabilized against thermal degradation and high temperatures. More particularly the invention concerns the use of additives that prevent the thermal decomposition of metal dialkyldithiophosphatcs in lubricating oil compositions under high temperature conditions.

It is well known to employ metal dialkyldithiophosphates in lubricating oil compositions for the purpose of improving the load carrying ability of the composition and to prevent wear. Normally, the use of such additives presents no serious problems when the concentration of the metal dialkyldithiophosphate is relatively low; i.e., in the range of about 0.1 to 0.5 wt. percent. It has recently been found however that, when it is necessary to increase the concentration of the additive to 1.0 wt. percent or more in certain compositions, there is a tendency for the metal dialkyldithiophosphates to decompose at high temperatures, causing the formation of heavy sediment and a strong odor and thus rendering the oil composition useless. This problem has arisen particularly in the case of marine turbine oils wherein cadmium salts of dialkyldithiophosphoric acids are employed to impart sulficient load carrying capacity to enable the oil to meet certain gear tests.

In order for a marine turbine oil to meet the specifications of the US. and Canadian Navies, its neutralization number must not exceed 0.2. It is possible to formulate a turbine oil meeting this specification which will, at the same time, have sufiicient load carrying ability to pass certain gear tests by incorporating into the composition a cadmium dialkyldithiophosphate. Preferably, the dialkyldithiophosphates are drived from secondary alcohols averaging at least about 4.5 carbon atoms per alkyl group and preferably from about 6 to 12 carbon atoms per alkyl group. Secondary alcohols having from 3 to about 20 and preferably from about 3 to 13 carbon atoms may be used in the preparation of these additives. Lubricating oil compositions containing up to about 3 wt. percent of a cadmium dialkyldithiophosphate of the type described will have an ASTM D974 neutralization number below 0.2. Lubricating oil compositions containing above about 1 to 1.25 wt. percent of this type of cadmium dialkyldithiophosphate will carry in excess of 3000 pounds in the Ryder gear test described in Military Specification MIL-L- l73 3lB (Ships) 4.6.2.

Use of the cadmium dialkyldithiophosphate in this range of concentrations will also enable oil compositions to meet the IA-E Gear Test requirement for specifications of both the British Navy (OEP-90) and the Canadian Navy (BGP-SS 8T) as well as the FZG Gear Test (Niemann Test) requirements for merchant fleet acceptance in Germany.

Other metals such as lead and nickel will also give low neutralization numbers of the order of 4 or 5 when employed in a lubricating oil composition as compared with a. neutralization number of about 180 in the case of the conventionally used antiwear agent zinc dialkyldithiophosphate.

While, as stated, it is possible to employ cadmium, nickel or lead dialkyldithiophosphate in lubricating oil compositions requiring high load carrying capacity and relatively low neutralization numbers, such compositions are limited in high temperature stability and tend to decompose ther- "ice mally under high temperature conditions such as exist in the Staeger oxidation test. The metal dialkyldithiophosphates tend to decompose and form sludge under such conditions.

In accordance with the present invention, it has been found that lubricating oil blends containing metal dialkyldithiophosphates can be effectively stabilized against thermal decomposition by incorporating therein a monoester of a trialkylolalkane of from about 6 to 12 carbon atoms and of a carboxylic acid selected from the group consisting of saturated and unsaturated fatty acids of from 12 to 20 carbon atoms and alkyl mercaptoacetic acids having alkyl groups of from about 9 to 18 carbon atoms. The monoesters that may be employed include those of trimethylolpropane, triethylolpropane and trimethylolbutane. The monoesters employed in the present invention are characterized by a neo structure. Specific examples are: trimethylolpropane monooleate, trimethylolpropane monostearate, triethylolpropane monosterate, triethylolbutane monolaurate, trimethylolpropane monopalmitate, and trimethylolpropane mono laurylmercaptoacetate.

The invention is particularly applicable to a marine turbine oil formulation containing a cadmium dialkyldithiophosphate in conjunction with a corrosion inhibitor of the type containing free carboxy groups. Corrosion inhibitors that have been found to be particularly useful in marine turbine oil formulations include mercaptoacetic acids having the formula: RSCH COOH, wherein R is a branched alkyl group containing in the range of 9 to 17 carbon atoms. Preferably R is a branched alkyl group of about 13 carbon atoms. Such branched chain alkyl groups may be derived from the well-known oxo alcohols which are prepared by reaction of olefins with carbon monoxide and hydrogen in the presence of a cobalt or similar catalyst to form aldehydes of one more carbon atom than the starting olefins, followed by catalytic hydrogenation to the corresponding alcohols.

Also useful as rust inhibitors in the compositions of this invention are the alkenyl succinic acids having the following general formula:

wherein R represents an unsaturated aliphatic radical having about 10 to 22, preferably about 12 to 18 carbon atoms. Compounds wherein R is saturated are similarly useful. Rust inhibitors of this type are well known to the art and are described in US. Patents, e.g., 2,124,628 and 2,133,- 734. In practice the R group is generally a mixture of varying chain length averaging about C to C Such compositions are preferred rust inhibitors for use in the lubricating oil compositions of this invention. The succinic acid or mercaptoacetic acid type rust inhibitors are used in concentrations in the range of 0.01 to 0.10 weight percent based on the total weight of the lubricating composition. Preferably, the concentrations of succinic acid type rust inhibitor are in the range of 0.03 to 0.05 weight percent of the total composition. Other rust inhibitors which may be used include dinonyl naphthalene sulfonates as described in US. Patent 2,764,548.

The dialkyldithiophosphoric acid salts of this invention are normally prepared by reacting the secondary alcohol or alcohol mixture containing a secondary alcohol with phosphorus pentasulfide certain additional steps are taken.

' monoester.

and then forming the cadmium salt by direct neutralization with cadmium oxide I %S S\ 2(RO);P\ CdO a CD (O )2 2 SE S 2 metric amounts of alcohol and phosphorus pentasulfide at a temperature in the range of 160 to 200 F., e.g., 185 to 190 F., for about 1 to 6 hours, e.g., about 3 hours. The acid will generally be filtered. The neutralization of the acid with CdO will be carried out at a temperature in the range of about 80' to about 200 F., e.g. 120 to 170 F. and will continue until the product is essentially neutral, about .1 to 6 hours, e.g., about 3 to 4 hours. It is understood that the temperatures and particularly the time of reaction will vary somewhat because of such factors as the size of the reactionmixture, the equipment being used, and so on. The product will usually be diluted with mineral -oil or other suitable solvent to form a concentrate more easily handled than the pure additive.

While satisfactory products have been prepared under a variety of conditions within the ranges set forth above, for most consistent production of a satisfactory additive These are: (1) the phosphorus content of the P 8 is kept under the theoretical value of 27.87 wt. percent, preferably below about 27.8, e.g., 26.04175; (2) the acid is blown free of H 8 with an inert gas, e.g., nitrogen, before neutralization; (3) elemental sulfur isadded to the acid immediately before the neutralization. The last item, (3) above, is not always necessary if the P S used in the acid preparation has a'phos phorus content toward the lower end of the range given in step ('1) above. Of these precautionary steps, (1) appearsmost important.

. The lubricating oils constituting the base stocks in the compositions of this invention are preferably mineral lubricating oils although synthetic oils may be used. Preferably the oil base has a viscosity in the range of 37 to 150 Saybolt seconds Universal at 210 F., a viscosity index in the range of 50 to '150, a flash point above 370 F., a pour point below 25 F. and a gravity in the range of 26 to 34 API. For turbine oil use a solvent neutral type of 'oil having a viscosity index in the range of 90 to 11 5 is generally preferred;

The mineral lubricating oils may be of any preferred type including those derived from the ordinary paraffinic,

naphthenic, asphaltic or mixed base mineral crude oils by suitable refining methods. Synthetic hydrocarbon lubricating oils may also be employed. Other synthetic oils include dibasic acid esters such as di-Q-ethyl hexyl sebacate, carbonate-esters, glycol esters such as C oxo acid diesters of tetraethylene glycol, and complex esters as for example the complex ester formed by the reaction of 1 mole of sebacic acid with 2 moles of tetraethylene glycol and 2 moles of 2-ethyl hexanoic acid. 7

The lubricating compositions of the invention will contain between about 0.1 and 3 wt. percent, preferably from about 1 to about 2 wt. percent, of metal dialkyldithiophosphate and from about 0.05 to about 0.5 wt. percent, preferably 0.1 to 0.2 wt. percent, of the trialkylolalkane The dithiophosphates may be used without diluent or as oil solutions or concentrates containing for example 50 to 90 wt. percent metal dialkyldithiophosphate.

r 4 Antifoamants are normally not required in the lubricating oil compositions of this invention. cone fluid may be used as an antifoamant if desired. The

silicone fluid, if used, will be used in concentrations ranging from 0.0001 to about 0.01 wt. percent based on the total weight of the composition. Of particular utility for obtaining additional antifoarning properties in the lubricants of this invention is Dow Corning Fluid 200.

For most applications theoxidation stability andload carrying ability imparted to the lubricating oil by the dithiophosphate additives of this invention will be entirely. adequate. In some specialized applications it may be desirable to include supplemental additives. Supplemental oxidation inhibitors include the phenolic and amine inhibir tors 'well known in the art, e.g., 2,6 di-t-butyl-p-cresol or phenyl-alpha-naphthylamine.

The nature of this invention will be more readily undera stood when reference is made to the accompanying exam ples illustrating the same.

EXAMPLE 1 Preparation of trim'ethylolpropane monool eate The following ingredients were changed to a4-necked distillation flask equipped with a stirrer, a thermometer, and graduated water trap with condenser:

268 grams trimethylolpropane 566 grams oleic acid 600 grams xylene The reactants were heated and stirred at reflux temperature for 10 hours, with nitrogen blowing to maintain an inert atmosphere. through the distillation trap throughout the course of the reaction; Thefollowing observations were madef Initial reflux temperature C 140 Final reflux temperature C 225 Total water drawn off cc 36 Total Xylene drawn off cc 654 Neut. Number of product (ASTM D -974) 6.0

distilled Water.

The organic layer was then vacuum stripped under a nitrogen blanket at 113 C. and 4 mm. Hg absolute pres- 7 sure. The neutralization number of the final product was 1.18 and the product yield was 612 grams.

EXAMPLE 2 Preparation of trimethylolpropane mono C 0x0 mercaptoacetate The following ingredients were charged to a 1 liter 4-necked flask equipped with a stirrer, a thermometer, and graduated water trap with condenser:

134 grams trimethylolpropane 289 grams C Oxo mercaptoacetic acid 300 grams xylene The reactants were heated with stirring at reflux temperature (142153 C.) for 4% hours at'which time 15.5 cc. of water had collected in the trap. The xylene was then stripped off under vacuum mm. Hg) at a maxi.- mum temperature of 168 C. The neutralization number of the final product was 7.77 and the product yield was 397 grams.

However, a sili- 7 Water and xylene were drawn 01f EXAMPLE 3 Preparation of dialkyldithiophosphoric acid After 450 grams of methyl isobutyl carbinol (MIBC) was heated in a reaction flask to 87 C., 245 grams of P 8 (containing 26.0% phosphorus) was added slowly over a period of 1 hour while holding the temperature at 87 C. The reaction was continued for a total time of 2 /2 hours. The product was then blown with nitrogen for /2 hour, cooled to 17 C., and filtered. The filtered product cont-ained 9.28% phosphorus and 18.8% sulfur, and had a neutralization number of 184.3.

EXAMPLE 4 Neutralization of acid In a reaction flask was placed 290 grams of the acid of Example 3. Then 75.4 grams of cadmium oxide was added slowly over a V2 hour period. The temperature rose to 58 C. during the addition. The temperature was further raised to 65 C. with the application of heat for a total reaction time of 3 /2 hours. To the reaction mixture were then added 116 grams of coastal extracted mineral oil and 12 grams of filter aid. After minutes stirring the reaction mixture was filtered through paper on a steam-heated Biichner funnel, precoated with additional filter aid. The filtrate was then dried by blowing with nitrogen under vacuum (150 mm. Hg) at 82 C. for one hour. The product was a clear, yellow, viscous liquid which, analyzed as follows:

Lubricating oil blends were prepared containing 1.25 wt. percent of the cadmium dialkyldithiophosphate concentrate of Example 4 and 0.035 wt. percent :of an alkenyl succinic acid corrosion inhibitor obtained commercially under the trade name Lubrizol-859. The base oil was of Mid-Continent origin, and had a viscosity of 210 F. of 59 S.S.U., a viscosity index of 105, and an API gravity of 30.2. The base oil also contained 0.0005 of a silicone anti-foaming agent (Dow Corning DC-200). To one of the blends was added 0.1 wt. percent of the additive of Example 1, to a second blend was added 0.1 Wt. percent of the additive of Example 2. Each of these blends was compared in the well-known Staeger oxidation test with a third blend containing no added monoester. The results obtained are shown in Table I.

TABLE I.STAE GER OXIDATION TEST DATA 1 1 230 F.; Cu catalyst. 2 75% concentrate of cadiurn di(1,3, dimethylbutyl) dithlophosphate. 3 Alkenyl succmic acid rust inhibitor (16 to 18 carbon atoms in alkenyl group).

4 Heavy sludge. B No sludge.

As shown in the data in Table I, the blend containing only the cadmium dialkyldithiophosphate and the corrosion inhibitor was seriously degraded at the end of 400 hours and gave heavy sludge. In each case where a monoester of the present invention was also incorporated,

sludging was prevented and color degradation was markedly reduced.

EXAMPLE 6 Blends similar to those of Example 5 were prepared using 1.5 wt. percent of the concentrate of Example 4 and the same amounts of rust inhibitor and anti-foaming agent as in Example 5. To one of these blends was added 0.2 wt. percent of trimethylolpropane monooleate and to another blend was added 0.2 wt. percent of polyethylene glycol di-tri-ricinoleate. Each of these blends, as Well as a blend containing no added ester, were subjected to the Staeger oxidation test. The results are given in Table II. It will be seen that, while the trimethylolpropane monooleate of the present invention prevented degradation of the oil in much the same manner as in Example 5, the polyethylene glycol ester was not nearly as eiiective in preventing degradation.

TABLE IL-STAEGER OXIDATION TEST [230 F.-copper catalyst] Tag-Robinson color after hours of test Initial 192 hours 400 hours 1:5% concentrate of cadmium di(1,3,dimethylbuty1) dithiophosb Algkeuyl succiuic acid rust inhibitor (16 to 18 carbon atoms in alkenyl group 0 Difierence in initial color is due to different sample of the base stock, which otherwise duplicated the base stock of Blend 1.

d Prepared in a manner similar to that for preparation of trnnethylolpropane monooleate as in Example 1.

Blend 2 of Table II gave a rating of 98 in the IAE Gear Test, thus meeting the minimum requirement of both the British and Canadian Navies. It also passed 12 load stages with no extreme Wear in the FZG Niemann Gear Test.

It is to be understood that the examples presented herein are intended to be merely illustrative of the invention and not as limiting it in any manner; nor is the invention to be limited by any theory regarding its operability. The scope of the invention is to be determined by the appended claims.

What is claimed is:

1. An improved marine turbine oil composition comprising a major proportion of a lubricating oil, from about 1 to about 3 wt. percent of an oil soluble cadmium salt of a dialkyldithiophosphoric acid having alkyl groups derived from secondary alcohols and containing from about 3 to about 20 carbon atoms per alkyl group with an average of at least 4.5 carbon atoms per alkyl group, and from about 0.05 to about 0.5 Wt. percent of a monoester of a nee-structured trialkylolalkane of from 6 to 12 carbon atoms and of a carboxylic acid selected from the group consisting of saturated and unsaturated fatty acids of from 12 to 20 carbon atoms and alkyl mercaptoacetic acids having alkyl groups of from 9 to 18 carbon atoms.

2. Composition as defined by claim 1 wherein said monoester is trimethylolpropane monooleate.

3. Composition as defined by claim 1 wherein said monoester is trimethylolpropane monostearate.

4. Composition as defined by claim 1 wherein said monoester is trimethylolpropane C oxo mercaptoacetate.

5. Composition as defined by claim 1 including from 0.005 to 0.5 weight percent of a corrosion inhibitor selected from the group consisting of alkyl mercaptoacetic acids having alkyl'groups of from 9 to 18 carbon atoms 2,603,653 7/52 Kosmin eta1. 25248.6 X 'and alkenyl succinic acids having from 10 to 20 carbon 2,884,379 4/59 Rudel et a1. 252--48.6' atoms in the alkenyl group. 1 2,911,367 11/59 Baus et a1; 252-32.7

R f db h E 3,013,971 12/61 Mastin 2s232.7

4 V 5S1??? 33311551 5233 FOREIGN PATENTS 536,837 2/57 Canada. 2,371,333 3/45 Johnston 252-486 2,477,356 7/49 Wayo 252-485 DANIEL E. WYMAN, Primary Examiner. 2,560,202 7/51 Zimrner et a1. 25233.4

2,601,063 6/52 Smith et a1 252-48.6 X JOSEPH LIBERMAN Examme" 

1. AN IMPROVED MARINE TURBINE OIL COMPOSITION COMPRISING A MAJOR PROPORTION OF A LUBRICATING OIL, FROM ABOUT 1 TO ABOUT 3 WT. PERCENT OF AN OIL SOLUBLE CADMIUM SALT OF A DIALKYLDITHIOPHOSPHORIC ACID HAVING ALKYL GROUPS DERIVED FROM SECONDARY ALCOHOLS AND CONTAINING FROM ABOUT 3 TO ABOUT 20 CARBON ATOMS PER ALKYL GROUP WITH AN AVERAGE OF AT LEAST 4.5 CARBON ATOMS PER ALKYL GROUP, AND FROM ABOUT 0.05 TO ABOUT 0.5 WT. PERCENT OF A MONOESTER OF A NEO-STRUCTURED TRIALKYLOLALKANE OF FROM 6 TO 12 CARBON ATOMS AND OF A CARBOXYLIC ACID SELECTED FROM THE GROUP CONSISTING OF SATURATED AND UNSATURATED FATTY ACIDS OF FROM 12 TO 20 CARBON ATOMS AND ALKL MERCAPTOACETIC ACIDS HAVING ALKYL GROUPS OF FROM 9 TO 18 CARBON ATOMS. 